Mounting of electrodes in electric discharge tubes



sept. 13, 1949. A. L. CHILCOT ET AL 2,481,906

MOUNTING OF ELECTRODES IN ELECTRIC DISCHARGE TUBES Filed Dec. 24, 1943Patented Sept. 13, 1949 MOUNTING OF ELECTRODES IN ELECTRIC DISCHARGETUBES Arthur Leslie Chilcot, Temperley, and Sydney Jackson, Chadderton,England Application December 24 1943, Serial No. 515,500

In Great Britain April 18, 1942 Section 1, Public Law 690, August 8,1946 Patent expires April 18, 1962 8 Claims. 1

This invention relates to electric discharge tubes of the type in whichat least one electrode is mounted at each end of the envelope, oneelectrode wholly or partially surrounding the other electrode orelectrodes.

For certain purposes discharge tubes of the usual type, in which all theelectrodes are carried by a common pinch, or foot, are undesirable.Examples of such purposes are where discharge tubes are required towithstand high mechanical stress, or to operate under such a condition,or for short-wave work, where inter-electrode capacity must be as low aspossible; for these purposes the type of tube in which an electrode ismounted at each end of the envelope is to be Dreferred. Where the tubehas a cathode activated by the deposition thereon of an alkali metal, itis also highly desirable that the tube be of the double-ended type inorder that the cathode may be maintained at low temperature whilst otherparts of the tube are heated to ensure that the alkali metal isdeposited only on the cathode.

Furthermore, the invention is concerned only with discharge tubes inwhich, in order to minimise the elfect of electric charges on the innerwall of the tube, one electrode wholly or partially surrounds the otherelectrode or electrodes.

Where such discharge tubes are produced in quantity by mass productionit has been found necessary to use such means as insulatinginterelectrode spacers in order to obtain products havingcharacteristics which vary as little as possible from one another. Ifsuch means are not employed wide variations of characteristics aredifficult to avoid due to relatively small variations of transversespacing. Where the cathode is to be activated as described above, suchspacers are objectionable owing to the likelihood of the formationthereon of conducting films which would cause electrical leakage betweenthe electrodes held by the spacers.

The main object of the present invention is to provide a form ofconstruction of electric discharge tube of the type stated which ensuresthat all products of the same manufacturing process are as nearlyidentical as possible to one another in respect of theircharacteristics, and which avoids the use of inter-electrode spacers.

The characteristics of such tubes are to a very great extent dependenton the transverse spacing between electrodes and the aim of theinvention is to ensure that such spacing is determined accuratelywithout the use of inter-electrode spacers. Thus, any variations in thecharacteristics which may still occur between the several products madein accordance with the invention are mainly those which arise from otherfactors, such as the chemical nature of the cathode surfaces and will berelatively small.

The invention is particularly useful for socalled midget tubes.

According to the invention an electric discharge tube has an envelopeformed wholly by a glass tube sealed at both ends and provided atpreselected parts with internal protuberances. By means of the apices ofsaid protuberances at least one electrode, which is mounted at one endof the said envelope, has been and is accurately located by aninterposed jig. Said apices serve to prevent both lateral and tiltingdisplacement of another electrode by contact therewith, said otherelectrode being mounted at the other end of the said envelope, in such amanner as at least partially to surround the said first-mentionedelectrode, whereby the said electrodes are accurately located in desiredtransverse spatial relationship to one another.

Also in accordance with the invention a method of constructing anelectric discharge tube includes the formation on pre-selected parts ofthe inner surface of a glass tube of protuberances the apices of whichare disposed in such a manner that when a jig holding at least oneelectrode is located by contact therewith, said jig is prevented fromundergoing both lateral and tilting displacement, sealing one end ofsaid tube to mount the said electrode whilst the said jig is so located,replacing the said jig by another electrode adapted at least partiallyto surround the said first-mentioned electrode and of such configurationas to be prevented by contact with the said apices from undergoing bothlateral and tilting displacement and sealing the other end of the saidglass tube to mount the said latter electrode, whereby the saidelectrodes are accurately located in desired transverse spatialrelationship to one another.

The invention includes the method of constructing an electric dischargetube of the type having a glass envelope in which is a first electrodemounted at one end of the envelope wholly or partially surrounded by asecond electrode mounted at the other end of the envelope, wherein theenvelope is deformed inwardly at small areas to a gauge so as to providelocating protuberances for the said second electrode, and wherein thesaid first electrode is temporarily located from such protuberances ofthe envelope whilst it is mounted in its end of the envelope, the secondelectrode being then inserted and mounted at the other end whilst heldin accurate transverse location relative to the first electrode by thesaid protuberances.

The term protuberances used herein is intended to mean projections of anapproximately conical or.hemi-spherical form.

Referring to the accompanying drawings:

Figs. 1, 2, 4, and 5 are longitudinal sectional views of a diode valveat various stages of its manufacture, in accordance with one-embodiment.

of the invention;

Fig. 3 is a cross-sectional view on the line A-A of Fig. 2, looking inthe direction of=the arrows;

Fig. 6 is a longitudinal sectional viewof a stage in the manufacture ofa diode valve inraccordance with another embodiment of the invention;-

Figs. 7, 8, and 9 are further details of modifications.

The invention may be carried intoeffect,

according to one form by way of example, in the manufacture of a diode.valve having a tubular anodeor firstelectrode and a surroundinghollowcylindrical cathode .or second electrode. .Aglass tube .a .of suitabledimensions, which is .to form the envelope, see Fig. 1, is placed on amandrel.

b thediameterof which is that of the cathode, and is'held coaxially withthe mandrel by means ofconese and .0 fittedinto thetwc ends; the

cones is attached rigidly to the mandrel whilst thecone c is slidableonthe mandrel, being held l against theend .of. the. tube a bya spring dbear.- ingagainst arime on the mandrel. ,Six. internal protuberances,.two .of. which are shown at f f are formed .in .the tube in. two setsof three, each.

set...of protuberances being...symmetrically disposed .on.. a -circle'and. the distance .between the twocirclesbeing lessthanthelengthof theoath? ode. The arrangement of. protuberances will be apparent fromFig's..1 and 3. The tube a issoftened locally by. the application .ofheat and each protuberance is, formed v.separately.by indenta-.

tion with a suitable .tool; the. glass is. allowed to -by the-apices ofthe protuberances f f and the tube is sealed by fusing the flangestogether. Thismethodofconstruction has certain manufacturing advantages.

vIf-itis,desired.to determine or fix the relative positionseof theelectrodes in an axial direction the jig k used to mount the anode maybe provided as shown'in Fig. 7 with a shoulder k to locate the anodeaxially against the protuberances'j nearest the open end of the tube. As

can be seen from Fig. 7 the jig has a recess is? adapted to receive andlocate..the..anode,-..the inner end. of .such recessbeingused.to..determine.-. the. axial position of the anode... Obviouslyif .usedforexample, .inplace of .the .jig. 7c of Fig. 4,.-.it.will

; be inserted from the right handend .ofihe tube.

' and its shoulder. k .willengage. and provide locacool between eachoperationin order. to .avoid I unwanted distortion of; the glasstube,The protuberances are formed to a height such.that their apices comeinto. contact. with mandrel b. After.

removalfrom the mandrel one end g of .the tube is..closed,andj'a ,holeblown in the middle of. this end asshownin Fig. 2.

The anode it, see Fig-4,consistsof a small tube of-hickel Weldedtoa wire.2 of suitable material upon which a glassbead 7' has been fused. Thisanode is held in.a jig khaving 'a diameter equal to, that of the.mandrel b and therefore also to that of .the cathode," and the jig isinserted in contact with the protuberances, f f*, in the glass tube a sothat the wirei passes through the hole in'th'e end g of the tube andwith the bead 7' adja- 1 cent thereto; Since the jig has a diameterequal to that of the "mandrel it is located-positively bythe--protuberances. The bead is-now fused to the end g of theglass-tube, thus mountingthe A anode-hrigidlyand-sealing the holein thatend of the tube. An exhaust tube 1 is also fused-into this sameend!WhencooL the jig 1c is removed through the other endofthetubeJe'aving:the A anode accurately located with respect to the apicesof'the protuberances.

The-cathode m, see Fig. 5, is in the formof a.

hollow cylinder having one end-'closedu A wire n 'of suitable material,welded to the centre of this :end,- carries a glass beads This glassbead is not 'shown as such, but. appears onlyi'as anpaextra'thickness-after fusing. The oathodexisinserted into: the tube: alandis:.located by the apices" of;

the protuberances f f thus .being brought into tion againsttheprotuberances. nearest. 251101]... end. Similarly .axial...location.may. .be...provided..- forthe cathode, thus .(as..shown..in Fig.., 8)-the:

,cathode m may .be. inserted. toa ,distance..deter-.

mined by-a protubel ancej ontube..a ,.of.greater.. height thantheprotuberanceson.the ,inner.wall.-. of the; envelope provided at. thecorrect-position... Aprotuberance: .asv shownat- F, on .tuhe.:ain.Fi'g.-.

-.;9 .for this .latter purpose-may also.-constitute. one..;

of, the protuberances: serving to .locate thegcatlh" ode. radially,,thus, forming-.- a single stepped? on shelved? protuberance: After.said electrode. iS sealed in,..the jig 1 is removed fromthe :openendnof thetubaand saidend-is then sealed.

The anode may be.-. mounted .asymmetrica-llxwith relation :to the.cathode by using :an. approe priately asymmetrical jig.Theahollow-cylindrical electrode may. be.;the anodelinsteadr-of. the.

cathode. Furthermore, .one'or -more-additional-.-

electrodes "may beinserted, being..-;held:in .the same or -otherxjigshaving.=.a diameter equaltitow that of the a cylindrical electrode sothat alllsuch electrodes-are located during mounting. .-fromztheprotuberances-r The cathode may -.be "of 'eithen.

the colelor hot emissive variety and .the-tube-may.- be gas-filled-orevacuated toany required-.degree.,

Theoperationof. :fusing the glass .envelope :at small-areas=anddeforming the same .to produce the protuberances.-. with or; i withoutsubsequent shaping: to form such protuberancesrequires onlyzl localheating. of.-.-shortduration :which: may be: done without: producinggeneral distortion: of.-the .7 envelope, esepcially where such fusing is-:done oneat a-time.:-- Consequently, suchnlocating pro-.-- tuberancesmay be formed to a-high degreerofe. accuracy-which they will maintainwhilst-the envelope-is subjectedelsewhere tdfurther proc-r essing;

Since only. -the apices of, a the. :protuberances--; touch .:,thecylindrical electrode; the.-latter-:may 1; be heated for de gassingpurposes withoutfusing; orrcracking the glassaenveloper especially; isthis;-.- so where a borosilicate glass is-employed.

Insteadaof using. six .protuberancesiarrangedr. as described above,any.;=,other :suitable arrange: ment ornumberzof' protuberances whichprevents a both lateral .-.-"and tilting 2 displacement of the. jig:.-;or h of. {the electrode in scontact therewith, asztthe:

:casemay be, smay'belemployed.1i.

It will be appreciated that whilst variations may occur in thedimensions of glass tubing, the dispositions of the apices of theprotuberances in the several products, being formed against anaccurately machined mandrel, are reproduced accurately. Since the jigand the hollow cylindrical electrode, being of metal, may also be formedwith considerable accuracy, it is possible them having identicalinter-electrode spatial relationships and hence uniformity ofcharacteristics subject only to any slight variation due mainly to otherfactors, such as the chemical nature of the cathode surface.

What we claim is:

1. A method of constructing an electric discharge tube which comprisesforming protuberances on pre-selected parts of the inner surface of aglass tube, the apices of said protuberances being disposed in such amanner that when a jig holding at least one electrode is located bycontact therewith, said jig is prevented from undergoing both lateraland tilting displacement, inserting said jig to so contact with saidapices, fusing to seal one end of said tube to mount a first electrodewhilst said jig is so located, removing said jig and inserting in placethereof a second electrode to at least in part surround said firstelectrode, contacting said second electrode with said apices so as toprevent both lateral and tilting displacement, and fusing the other endof said tube to seal the same and to mount said second electrode,whereby said electrodes are accurately located in desired transversespatial relationship to one another.

2. A method of constructing an electric discharge tube which comprisesforming protuberances on pre-selected parts of the inner surface of aglass tube, said protuberances being symmetrically disposed on a circle,the apices of said protuberances being disposed in such a manner thatwhen a jig holding at least one electrode is located by contacttherewith, said jig is prevented from undergoing both lateral andtilting displacement, inserting said jig to so contact with said apices,fusing to seal one end of said tube to mount a first electrode whilstsaid jig is so located, removing said jig and inserting in place thereofa second electrode to at least in part surround said first electrode,contacting said second electrode with said apices so as to prevent bothlateral and tilting displacement, and fusing the second end of said tubeto seal the same and to mount said second electrode, whereby saidelectrodes are accurately located in desired transverse spatialrelationship to one another.

3. A method of constructing an electric discharge tube which comprisesforming two sets of three protuberances on pre-selected parts of theinner surface of a glass tube, the protuberances of each set beingsymmetrically disposed on different circles the apices of saidprotuberances being disposed in such a manner that when a jig holding atleast one electrode is located by contact therewith, said jig isprevented from undergoing both lateral and tilting displacement,inserting said jig to so contact with said apices, fusing to seal oneend of said tube to mount said electrode whilst said jig is so located,removing said jig and inserting in place thereof another electrode to atleast in part surround said first electrode, said second electrode beingof a length greater than the distance between said circles, contactingsaid other electrode with said apices so as to prevent both lateral andtilting displacement, and fusing the other end of said tube to seal thesame and to mount said other electrode, whereby said electrodes areaccurately located in desired transverse spatial relationship to oneanother.

l. A method of constructing an electric discharge tube which comprisesforming protuberances on pre-selected parts of the inner surface of aglass tube, said protuberances being formed by inserting a mandrel insaid tube, locally softening said tube, exteriorly indenting saidsoftened areas to cause contact of said protuberances with said mandreland removing said mandrel, the apices of said protuberances beingdisposed in such a manner that when a jig holding at least oneelectrodeis located by contact therewith, said jig is prevented from undergoingboth lateral and tilting displacement, inserting said jig to so contactwith said apices, fusing to seal one end of said tube to mount a firstelectrode whilst said jig is so located, removing said jig and insertingin place thereof a second electrode to at least in part surround saidfirst electrode, contacting said second electrode with said apices so asto prevent both lateral and tilting displacement, and fusing the otherend of said tube to seal the same and to mount said second electrode,whereby said electrodes are accurately located in desired transversespatial relationship to one another.

5. A method of constructing an electric discharge tube of the typehaving a glass envelope in which a first electrode mounted at one end ofthe envelope is at least partially surrounded by a second electrodemounted at the other end of the envelope which comprises inserting amandrel within said envelope, forming protuberances for said secondelectrode on the inside of said envelope at small areas and to an extentdetermined by said mandrel, removing said mandrel, inserting said firstelectrode at said one end and adjusting the position thereof relative tosaid protuberances, fusing said first electrode in place, then insertingsaid second electrode in the opposite end of said envelope into contactwith said protuberances and fusing said second electrode in place.

6. A method of constructing an electric discharge tube of the typehaving a glass envelope in which a first electrode mounted at one end ofthe envelope is at least partially surrounded by a second electrodemounted at the other end of the envelope which comprises insertin amandrel within said envelope, forming protuberances for said secondelectrode on the inside of said envelope at small areas and to an extentdetermined by said mandrel, said protuberances being symmetricallydisposed on a circle, removing said mandrel, inserting said firstelectrode at said one end and adjusting the position thereof relative tosaid protuberances, fusing said first electrode in place, then insertingsaid second electrode in the opposite end of said envelope into contactwith said protuberances and fusing said second electrode in place.

7. A method of constructing an electric discharge tube of the typehaving a glass envelope in which a first electrode mounted at one end ofthe envelope is at least partially surrounded by a second electrodemounted at the other end of the envelope which comprises inserting amandrel within said envelope, forming protuberances for said secondelectrode on the inside of said envelope at small areas and to an extentdetermined by said mandrel, said protuberances being formed in two setsof three protuberances, the

prntuberances of each-set beingsymmetrically disposed on aJeircleandzthe distance between the two circles: being .lessrth'an the lengthof said second electrode, removing said mandrel; inserting said firstelectrode at said one endiand adjusting .theposition thereof relative to:said protuberances, fusing said electrode: in place, then insertingsaid second electrode in the opposite end of said envelope into contactwith said protuberances and fusing-"said second: electrode in/place.

.8.v A.;meth0d of constructing an: electric discharge tube of thetypehaving a-glass envelope in-.which a first electrode :mounted atone'end of the envelope isat least partially surrounded-by asecondelectrode-mountedaat theother end of the-envelope which comprisesinserting a mandrel-within said envelope, forming protuberances forsaid: second electrode on the inside of said envelope at small areasandto an extent determined by saidmandrel, said protuberances beingformed: by locally softening= said envelope, exteriorlyzindenting saidsoftened areas to cause contact of said protuberances with said mandrel,removing said-mandrel, inserting said first electrode at said oneend'andzadjusting the position thereof relative to said protuberances,fusing said first electrode'in place, then inserting said's'econdelectrode in the opposite end of said-envelope into contact with saidprotuberances and fusing said second electrode in place.

ARTHUR LESLIECHIL'GOT.

SYDNEY JACKSON.

1 REFERENCES CITED The following'references are'of record in the file ofthis patent:

UNITED STATES PATENTS

